'\" et
.TH READONLY "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
readonly
\(em set the readonly attribute for variables
.SH SYNOPSIS
.LP
.nf
readonly name\fB[\fR=\fIword\fB]\fR...
.P
readonly\fR -p
.fi
.SH DESCRIPTION
The variables whose
.IR name s
are specified shall be given the
.IR readonly
attribute. The values of variables with the
.IR readonly
attribute cannot be changed by subsequent assignment, nor can those
variables be unset by the
.IR unset
utility. If the name of a variable is followed by =\c
.IR word ,
then the value of that variable shall be set to
.IR word .
.P
The
.IR readonly
special built-in shall support the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 12.2" ", " "Utility Syntax Guidelines".
.P
When
.BR \-p
is specified,
.IR readonly
writes to the standard output the names and values of all read-only
variables, in the following format:
.sp
.RS 4
.nf

"readonly %s=%s\en", <\fIname\fR>, <\fIvalue\fR>
.fi
.P
.RE
.P
if
.IR name
is set, and
.sp
.RS 4
.nf

"readonly %s\en", <\fIname\fR>
.fi
.P
.RE
.P
if
.IR name
is unset.
.P
The shell shall format the output, including the proper use of quoting,
so that it is suitable for reinput to the shell as commands that
achieve the same value and
.IR readonly
attribute-setting results in a shell execution environment in which:
.IP " 1." 4
Variables with values at the time they were output do not have the
.IR readonly
attribute set.
.IP " 2." 4
Variables that were unset at the time they were output do not have a
value at the time at which the saved output is reinput to the shell.
.P
When no arguments are given, the results are unspecified.
.SH OPTIONS
See the DESCRIPTION.
.SH OPERANDS
See the DESCRIPTION.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
None.
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
See the DESCRIPTION.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
.IP "\00" 6
All
.IR name
operands were successfully marked readonly.
.IP >0 6
At least one
.IR name
could not be marked readonly, or the
.BR \-p
option was specified and an error occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH EXAMPLES
.LP
.nf
readonly HOME PWD
.fi
.SH "RATIONALE"
Some historical shells preserve the
.IR readonly
attribute across separate invocations. This volume of POSIX.1\(hy2017 allows this behavior,
but does not require it.
.P
The
.BR \-p
option allows portable access to the values that can be saved and then
later restored using, for example, a
.IR dot
script. Also see the RATIONALE for
.IR "\fIexport\fR\^"
for a description of the no-argument and
.BR \-p
output cases and a related example.
.P
Read-only functions were considered, but they were omitted as not being
historical practice or particularly useful. Furthermore, functions must
not be read-only across invocations to preclude ``spoofing''
(spoofing is the term for the practice of creating a program that acts
like a well-known utility with the intent of subverting the real intent
of the user) of administrative or security-relevant (or
security-conscious) shell scripts.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.14" ", " "Special Built-In Utilities"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 12.2" ", " "Utility Syntax Guidelines"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
